THE HISTORICAL RECORD OF METAL ENRICHMENT IN 2 FLORIDA ESTUARIES

Historical Profiles of metal accumulation have been generated for the lower St. Johns River and Hillsborough Bay, Florida, in cores represen ting approximately 50 yr of sediment and metal accumulation. These pro files demonstrate that Cd, Pb, and Zn are enriched in these Florida es tuarine sediments. Pb enrichment has decreased since the mid 1970s bec ause of reduced use of leaded gasoline. In the St. Johns River, most m etals exhibit a trend of increasing enrichment with time. Cd enrichmen t significantly decreased between 1970 and 1975 as a result of reduced discharges into the river and control of aquatic vegetation. In Hills borough Bay, enrichment factors for most metals are relatively high an d show little change downcore. Cr, Cu, and Ni border on enrichment and Pb, Cd, and Zn are enriched. The results of this study are consistent with other studies of surficial-sediment metal concentration in other Florida estuaries.